Each year, a great number of people risk vision loss from conditions involving vitreous traction. Vitreous traction results from changes in the mechanical properties of the vitreous body of the eye. Vitreous traction may act to deform the retina or detach the retina from underlying layers of the eye. If such a condition is left untreated, the retina may degenerate with resulting vision loss. Thus, early and accurate diagnosis of conditions involving the vitreous and retina is essential to determine appropriate treatment to correct or limit progression of the condition and preserve vision.
Unfortunately, many retinal disorders are associated with hemorrhage which prevents visual diagnosis. In these cases diagnosis is currently performed by ultrasonic imaging of the transient vitreal motion resulting from an ocular saccade. (See, Michaels, et al, Retinal Detachment, 1-1138 (The C.V. Mosby Company, St. Louis, 1990) and Byrne, Ultrasound of the Eye and Orbit, 1-505 (Mosby Year Book, St. Louis, 1992), the entire content of each being expressly incorporated hereinto by reference). Disturbances in vitreal motion indicate points of vitreoretinal adhesion, aiding localization and diagnosis of retinal conditions. However, eye motion makes localization of small targets difficult.
More specifically, in conventional ocular kinetic echography, a standard B-mode imaging system is used to observe motion in the vitreous induced by movement of the eye. The transducer is placed on the eye and the patient is asked to move their eye. This eye movement generates inertial movement of the vitreous. When the eye movement stops, the vitreous continues to move for a short period of time. It is during the eye movement and after movement that the clinician observes the B-mode image for any disturbances in the vitreal motion which may indicate the location of vitreoretinal adhesions which cannot easily be visualized using static ultrasound. During movement and after movement the clinician may also assess the degree of vitreoretinal adhesion at a particular lesion such as a retinal tear. Unfortunately after movement lasts approximately two seconds, so the time available to observe vitreal motion is brief. Also, every eye movement tends to move the region of interest out of the imaging plane and cause probe movement and loss of registration between successive images, making detection and localization of vitreoretinal adhesion extremely difficult.
Recently, a technique has been disclosed in U.S. Pat. No. 5,487,387 to Trahey et al (the entire content of which is expressly incorporated hereinto by reference) whereby solid masses and fluid-filled cysts may be distinguished using an ultrasonic transducer to transmit a plurality of ultrasonic signals into a target lesion within a human body and receive a plurality of reflected signals therefrom. At least one of the plurality of transmitting signals should be of sufficient intensity to initiate movement of any fluid located with the target lesion. A comparison is made of the differences between individual ones of the plurality of reflected signals to detect the presence or absence of fluid movement within the target lesion. Thereafter, a determination may be made as to whether the target lesion is a fluid-filled cyst or a solid mass based upon the presence or absence of fluid within the target lesion.